This invention relates generally to signal amplifying circuitry and more particularly to an improved low noise feedback amplifier employing a gallium arsenide field effect transistor.
Advantages of the employment of field effect transistors of the gallium arsenide type are now quite widely exploited in circuitries which function to provide low noise amplification at ultra high frequencies and microwave frequencies. Due to the greater carrier mobility inherent in gallium arsenide field effect transistors, a greater carrier mobility is experienced and transit time is reduced, with the result that high frequency performance improvements are realized.
Because of the low noise, high gain and good dynamic range traits exhibited by field effect transistors, their employment in high performance receiver circuitries is desirable as compared to the employment of bipolar transistors.
Known biasing arrangements for gallium arsenide field effect transistors are complicated by the necessity of preventing high current from reaching the drain electrode of the field effect transistor. Such known biasing methods employ circuitries necessitating numerous components whereby, for example, negative biasing voltage is applied to the gate electrode of the gallium arsenide field effect transistor first, and then followed by the application of positive voltage to the drain. Such biasing methods are also known to employ capacitors and radio frequency chokes in circuit with the biasing source through which the bias potential is applied to the drain and gate electrodes of the gallium arsenide field effect transistor.
It is further realized in the art employing gallium arsenide field effect transistors for wideband operation, that negative feedback is required and that one of the prime areas of difficulty in amplifier design lies in controlling the impedance match between devices.